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Om jag minns rätt: Fjäderns hårdhet bestämmer hur mycket av trycket som ska gå till bakbromsarna

Denna text skamlöst lånad från Haynes wrongual 
1 On models fitted with front disc brakes a pressure regulator is installed which affects the operation of the rear brakes.
  This is because disc brakes have a more powerful braking action and accentuate the 'nose-dipping' attitude of the vehicle
  when sharp braking is used. This in turn lightens the load on the rear wheels and in certain circumstances
   when the vehicle is empty could cause the rear wheels to lock.
   The pressure regulation takes into account the rate of deceleration and the 'nose-dip' inclination and correspondingly
    reduces the pressure in the hydraulic system acting on the rear wheel cylinders if necessary.
2 The regulator consists of a ball in an inclined chamber and
two spring loaded subsidiary pistons which act as pressure
reducers. The angle of the inclined chamber depends on the
position of the vehicle body. Consequently a loaded vehicle will
not increase the angle so much as an empty one. When braking
occurs the ball is thrown forward and depending on the rate of
deceleration and the angle up which it has to roll it shuts off the
direct fluid flow to the rear brake cylinders. Pressure is then
applied to two intermediate pistons of different diameters, with
a spring between them which effectively reduces the output
pressure to the rear brakes.
3 Malfunction of the unit will result in either locking of the
rear wheels or, at the other extreme, ineffective braking. It is not
possible to test the regulator accurately without having the
suitable hoses and gauges up to 1500 p.s.i. to connect to the
front and rear brake circuits. When the front circuit pressure is
1420 p.s.i. the regulated pressure at the rear should be 780 - 925
p.s.i.
4 The regulator is mounted on the side frame member on the
inside at the rear underneath. It is easily removed and replaced.
The hydraulic line unions are disconnected and the securing
screws taken out. The residual pressure valve screwed into the
front end should be removed for fitting to a new unit as
required.